1. Field of the Invention
The present invention relates to a toner, a method for producing a toner, a fixing method using the toner, an image forming method, and an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses, such as printers, facsimiles and copiers, are apparatuses for forming images including characters and symbols on a recording medium such as paper, clothes and OHP sheets, based on image information. In particular, electrophotographic image forming apparatus enable forming high-definition images on regular paper at high speed, and thus they are widely used in offices. In such electrophotographic image forming apparatuses, the heat fixing method, in which a toner on a recording medium is heated to be melted and the melted toner is pressurized to thereby fix the toner on the recording medium, is widely used. The heat fixing method is preferably used because it can provide high fixing speed and high quality of fixed images and the like.
However, about half or more of the electric power in such an electrophotographic image forming apparatus is consumed by heating a toner in the heat fixing method. Meanwhile, from the viewpoint of environmental preservation in recent years, a fixing device of low (energy-saving) electric power consumption is desired. That is, a fixing method which enables extremely lowering the temperature of heating a toner for fixing the toner more than in the past or a fixing method which requires no heating a toner is desired. Particularly, a non-heating fixing method of fixing a toner on a recording medium without heating the toner at all is ideal in terms of low electric power consumption.
As such a non-heating fixing method, for example, Japanese Patent (JP-B) No. 3290513 proposes a wet-process fixing method in which an oil-in-water type fixing agent, in which an organic compound capable of dissolving or swelling a toner and being insoluble or sparsely soluble in water is dispersed in and mixed with water, is sprayed or dropped in the form of droplets on a surface of a fixing target material having an unfixed toner and provided at a predetermined position so as to make the toner dissolved or swollen, and then the fixing target material is dried.
However, in the wet-process fixing method of Japanese Patent (JP-B) No. 3290513, a fixing agent, in which the organic compound insoluble or sparsely soluble in water is dispersed in and mixed with water, is used, and thus when a large amount of the fixing agent is applied to a toner, a recording medium (fixing target material) such as transfer paper absorbs the moisture in the fixing agent, causing wrinkles and curling of the recording medium. Because of this shortcoming, stable and high-speed conveyance of a recording medium required for an image forming apparatus is considerably impaired. If an attempt is made to remove the moisture from the fixing agent that has been applied onto the recording medium by evaporating a large amount of water contained in the fixing agent, using a drier, it will require electric power equivalent to the electric power consumption of an image forming apparatus using a heat fixing method.
As a fixing agent which is nonrepellent to an unfixed toner having been subjected to water-repellent treatment, some fixing agents have been conventionally proposed, in which a material making a toner dissolved or swollen is dissolved in an oil-based solvent. As one of them, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-109749 proposes a fixing liquid in which a material which makes a resin component constituting a toner dissolved or swollen, such as aliphatic dibasic acid ester, is diluted with (dissolved in) dimethyl silicone as a nonvolatile diluent (solvent). In addition, as a fixing solution which can be used in a fixing method by which an unfixed image formed by an electrostatic method can be easily fixed on an image-receiving sheet with high definition, without disturbing the image, Japanese Patent Application Laid-Open (JP-A) No. 59-119364 proposes an unfixed toner image-fixing solution, in a miscible state, in which 8 volume parts to 120 volume parts of silicone oil is mixed in 100 volume parts of a solvent having compatibility with the silicone oil. Since such an oil-based fixing liquid contains an oil-based solvent having high affinity to an unfixed toner having been subjected to repellency treatment, it can make a toner dissolved or swollen without rejecting the unfixed toner having been subjected to repellency treatment and can make the toner fixed on a recording medium.
However, the methods disclosed in Japanese Patent (JP-B) No. 3290513, Japanese Patent Application Laid-Open (JP-A) Nos. 2004-109749, and 59-119364 have a problem that a toner is offset to a fixing agent-coating unit due to a surface tension of the fixing agent when a coated film is formed extremely thin, because the fixing liquid is applied onto the recording medium. In contrast, when the coated film is formed extremely thick, the fixing liquid in an excessive amount is applied onto a recording medium, and toner particles are flowed away by the flow of the fixing agent, resulting in degradation in image, the occurrence of curling of the recording medium and a paper jam in an image forming apparatus.
Then, as a fixing method capable of simultaneously solving the above-mentioned various problems, Japanese Patent Application Laid-Open (JP-A) No. 2009-8967 proposes to fix a foam-like fixing liquid and to control the foam-like fixing liquid to a desired value.
However, even with use of the proposal, it cannot be said that sufficient fixability is achieved, and there are increasing demands for further improvements in fixing a toner.
In the meanwhile, as a method of strongly improving the properties of toner to be fixed on a recording medium using a fixing liquid as described above, Japanese Patent Application Laid-Open (JP-A) No. 2008-139504 discloses a toner-fixing method using a toner having a ΔTg (a variation in glass transition temperature) of 30° C. or higher in the DSC measurement when a softening agent is added in an amount of 3% by weight to the toner. With use of the fixing method disclosed in JP-A No. 2008-139504, it is possible to sufficiently soften the toner even when a small amount of a softening agent is used, because the compatibility between the toner and the softening agent is sufficient, and thus the fixing method is sufficient to speed up the fixing speed. That is, the fixing method enables high-speed fixing operation in the light of improving the compatibility of a toner and a softening agent.
However, higher fixing speed operation is desired, and to respond to the demands, there is a need to take an approach from other standpoints.
Further, in such a fixing method, in order to fix a toner on paper, it is necessary to sufficiently soften the toner as well as to rapidly soften the toner through penetration of a fixing liquid containing a softening agent, and when the softened state of a toner is insufficient or nonuniform, or when the softening speed is slow, there is a problem that a sufficient strength of the toner against paper cannot be obtained particularly in high-speed printing, easily causing peel-off in particular of halftone images.
The present invention aims to solve the above-mentioned conventional problems and to achieve the following object. That is, an object of the present invention is to provide a toner which is capable of obtaining images having high strength immediately after being fixed with the toner regardless that the consumption energy is extremely small in a fixing step and having strong abrasion resistance (even in halftone images) and which is also excellent in heat-resistant storage stability; a fixing method, an image forming method and an image forming apparatus each using the toner.
The present invention also aims to provide a method for producing a toner by which the toner can be stably produced so as to have small particle diameters and a sharp particle size distribution.